Some semiconductor devices comprise memory devices that are used to store information. A recent development in semiconductor memory devices is magnetic random access memory (MRAM) devices. MRAM devices comprise conductive lines (word-lines and bit-lines) positioned in different directions, e.g., perpendicular to one another in different metal layers. The conductive lines sandwich resistive MRAM cells that comprise magnetic tunnel junctions (MTJs), which function as magnetic memory cells. An MRAM cell is a form of non-volatile memory capable of storing bits of digital information (binary 0's or 1's). MRAM digital data is not stored as an electrical charge as in traditional RAM components, rather the bit state (being 0 or 1) is stored via resistive states (high resistance or low resistance) or magnetic states in magnetic storage elements such as MTJs which do not require constant electrical power to retain their state.
In a read operation of a MRAM cell, the information is read by sensing the magnetic state (resistance level) of the MTJ through a sensing current flowing through the MTJ. For a write operation of a MRAM cell, the information is written with change of the magnetic state to a predefined one by applying current to the MTJ to switch the magnetization of the MTJs. For an MTJ to change states, the current through the MTJ must be greater than a critical switching current of the MTJ and a higher switching current is required for faster switching. For an MTJ with a lower critical switching current, a lower switching current can be used for the write operation of the MTJ so the power consumption is reduced. Therefore methods of reducing critical switch current of an MTJ are of interests.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.